The purpose of this Program Project is to explore the nature and etiology of developmental language disorders, by following those disorders longitudinally from their point of origin, from prespeech through the major milestones of language development. The populations chosen for study are all known to be at risk for moderate to severe language impairment (LI) in the early years; all can be identified in the first or second year of life and followed to 5 - 6 years of age, when many will enter the school system. Our research to date suggests that some of these children go on to overcome early delays in language, while others continue to lag behind. The Program Project is designed to maximize our understanding of the linguistic, cognitive, affective and neural factors associated with these contrasting patterns of recovery and delay. Project 1 will focus on "late talkers" (LT) identified in the second year of life; previous research suggests that approximately 40% of these children will qualify for a clinical diagnosis of LI within the period of study. Project 2 will follow infants with different forms of early focal brain injury (FL), including injury to the classical language areas, providing us with a prospective look at the reorganizational processes that underlie recovery from deficit in this group. Project 3 will compare Williams Syndrome (WMS), a rare form of mental retardation in which language abilities eventually surpass other cognitive domains, and Down Syndrome (DNS), a profile of retardation that complements WMS in many respects; this project provides a unique opportunity to study the "fractionation" of language and cognition. Project 4 focusses on infants and toddlers with prenatal exposure to cocaine and/or methamphetamine; our past research suggests that many of these children are markedly delayed in linguistic and social functioning during the preschool years, and thus may constitute a new and growing form of early language impairment. Project 5 will explore the neural correlates of these contrasting profiles, through detailed electrophysiological studies of brain activity associated with linguistic and non-linguistic stimuli at each stage of development. By focussing on associations and dissociations between language and other cognitive and communicative systems, we will be in a position to test two competing theories of language and language disorders: "linguistic modularity" (i.e. the theory that language is acquired and maintained by a "special" faculty that is independent from the rest of mind and brain) vs. "linguistic functionalism" (i.e. the theory that language is acquired and maintained by mental/neural processes that language shares with other perceptual, cognitive and affective domains). The projects are served by 3 core facilities: Administration & Statistics (A), Biomedical Diagnostic (B), and Behavioral Diagnostic (C). In addition, all projects will draw from a common pool of experimental methods, permitting systematic comparisons by age, domain and population. The Program Project is administered by the UCSD Center for Research on Language, in association with seven UCSD academic departments, the SDSU Departments of Psychology and Communicative Disorders, Children's Hospital Research Center (CHRC), and the Salk Institute for Biological Studies.